What's the difference between XF's internal, external data directories?

[DavidJCobb]

As part of an add-on that I'm building, users need to be able to upload images for temporary storage, and admins need to be able to upload images for long-term storage. I currently store the user uploads in a subfolder in the external data directory, but I don't know whether to use the external or internal data directory for the admin uploads.

What exactly are the differences between the external and internal directories, and when would I use the internal one? :\

 

[Paul B]

Do you mean the /data and /internal_data directories?

One is public and contains the thumbnails (data).
The other is permission enabled and contains the original files (internal_data).